Electric valve circuit



Jul 8, 1941. c. c. HERSKIND 2,248.626

ELECTRIC VALVE CIRCUIT Filed May 23. 1940 Fig. I.

VOLTAGE 0F WINQING 22 I CURREN1 THROl/Gh' cwmaL MEMBER :7

C c nnsur THROUGH I LECTRODE I8 Inventor: Carl C. Herskind,

His Attorney.

Patented July 8, 1941 ELECTRIC VALVE CIRCUIT Carl C. Herskind, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application May 23, 1940, Serial No. 336,750

7 Claims.

My invention relates to electric valve systems and more particularly to control or excitation systems for electric valve apparatus of the type employing an ionizable medium, such as a gas or a vapor. in U. S. Patent 2,069,283 of Slepian et al. granted February 2, 1937, employ make-alive or immersion-ignitor control members comprising a material, such as boron-carbide or silicon-carbide, in contact with the mercury pool cathode to initiate an arc discharge within the electric valve means and, hence, control the energization of an associated load circuit. In accordance with the teachings of my invention described hereinafter, I provide new and improved control or excitation circuits for electric valve equipment of this nature.

It is an object of my invention to provide new and improved control or excitation systems for electric valve apparatus.

It is another object of my invention to provide new and improved-control or excitation circuits for electric valve apparatus of the type employing immersion-ignitor or make-alive electrodes.

It is a further object of my invention to provide new and improved excitation circuits for electric valves employing immersion-ignitor control members whereby positive control of the conductivities of the electric valves is effected without imposing an inordinate duty on the control members, and which thereby affords conditions favorable to increase the life of the electric valves.

Briefly stated, in the illustrated embodiments of my invention I provide new and improved excitation or control circuits for energizing the immersion-ignitor control members of the electric valve means and which comprise an energizing circuit which is oscillatory. The natural oscillation frequency of the control circuit is substantially greater than that of the voltage applied to the anode-cathode circuit so that only a pulse of current of relatively short duration is transmitted to the control member. An electric discharge device of the controlled type is connected between the control circuit and the control member to assure that only a single positive unidirectional impulse of current is transmitted to the control member. The electric valve means is provided with an auxiliary electrode which is also connected to the control circuit and which conducts current as soon as an arc discharge is established within the electric valve means, effecting transfer of current from the control member as soon as it has performed its function of initiating an arc discharge and in this manner reducing the duty Electric valves of the type disclosed imposed on the electric valve means and increasing its life.

For a better understanding of my invention, reference may be had to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. Fig. l diagrammatically illustrates an embodiment of my invention as applied to a double three-phase rectifier system, and Fig. 2 represents certain operating characteristics thereof. Fig. 3 represents a modification of the arrangement shown in Fig. 1.

Referring now to Fig. 1 of the drawing, I have diagrammatically illustrated my invention as applied to an electric valve converting system, such as a rectifier, for transmitting power between an alternating current supply circuit I and a direct currentcircuit, comprising conductors 2 and 3, through an inductive network, such as a transformer 4, comprising primary windings 5 and groups of secondary windings 6 and I. The secondary windings 6 and 1 may be arranged so that the system operates as a double three-phase system having neutral points of the respective groups of secondary windings interconnected through an interphase transformer 8. Connected in the translating apparatus are a plurality of electric valve means 9- of the type comprising an ionizable medium, such as a gas or vapor, capable of supporting an arc discharge and each comprises an anode I5, a cathode of the self-reconstructing type such as a mercury pool cathode l6, and an associated make-alive or immersionignitor control member I1 having an extremity thereof associated with the cathode [6. The immersion-ignitor control member I! is of the type having a specific electrical resistivity large as comparedwith that of the associated mercury pool and is preferably constructed of a material, such as boron-carbide or silicon-carbide. Each of the electric valve means 9l4 also includes an auxiliary electrode l8, the function of which will be explained hereinafter.

As an agency for supplying to the control members I1 impulses of current to render the electric valve means 9-H conductive in a predetermined order and to render them conductive at precise times during the cycles of anode-cathode voltages, I provide a plurality of excitation circuits each associated with a dilferent meet the electric valve means, and of which excitation circuit is is representative. It Will be understood that while only excitation circuit l9 associated with electric valve means 9 is illustrated, that the electrio valve means Iii-l4 are also provided with similar control or excitation circuits.

Excitation circuit is may be energized from a suitable source which may be alternating. For example, in Fig. 1 the excitation circuit is is illustrated as being energized from a source of alternating current constituting a winding 22 of a transformer 26 having primary windings 2i and secondary windings 2243, inclusive. A neutral connection 28 is connected to the common juncture of cathodes 16 of electric valve means a-m. The phase of the voltage induced in winding 22 may be adjusted by any suitable means, such as a rotary phase shifting device 23, when the trans former 2D is energized from the alternating current circuit l or from any other suitable source of current.

Excitation circuit l9 also comprises a capacitance 33 which is energized from the secondary winding 22 through a resistance 3i. I provide an oscillatory circuit for energizing the control member ll of electric valve means 9 and which constitutes a part of the excitation circuit is. This oscillatory circuit comprises an inductance 32 which with the capacitance 39 has a natural oscillation frequency substantialiy greater than the frequency of circuit I. I have found that when this excitation circuit is used in systems having a commercial frequency of the order of magnitude of sixty cycles per second, the system operates very satisfactorily when the natural oscillation frequency of the circuit comprising capacitance 3D and inductance 32 is of the order of magnitude of 1500 cycles per second. Connected in the oscillatory circuit I also provide a resistance 33 and an electric discharge device 34 which is also preferably of the type employing an ionizable medium, such as a gas or a vapor, and which is provided with a control member or grid 35. The electric discharge device 34 not only serves to effect energization of the associated control member I? at the desired times during the applied cycles of anode-cathode voltage, but also assures a single Luiidirectional energization of the control member If. able connection 36 between the common juncture 32' of inductance 32 and resistance 33 and the auxiliary electrode l8 ofelectric valve means 9. This connection serves to by-pass the current from the control member I? to the auxiliary electrode 18 as soon as an arc discharge is established within the electric valve means 9.

A plurality of control circuits is also provided for the electric discharge device 34 in the excitation circuit 19. for the electric discharge device 34 is energized from a transformer 38 comprising primary windings 39 and a plurality of secondary windings id. A suitable current limiting resistance M and a source of negative unidirectional biasing potential, such as a battery 42, may be connected to control'grid 35 of electric discharge device 33. The time at which the electric discharge device 34 conducts current and, hence, the time at which electric valve means 3 is rendered conducting, may be controlled or adjusted by means of a suitable control device, such as a rotary phase shifter 13 connecting transformer 33 and the alternating current circuit I.

The operation of the embodiment of my invention shown in Fig. 1 will be explained by considering the system when it is operating as a polyphase rectifier to transmit unidirectional current to the load circuit, comprising conductors I also provide a suit- For example, control circuit 31 2 and 3, from the alternating current circuit I, through transformer 4 and electric valve means 9-H. Due to the connection of the secondary windings G and 'I- through interphase transformer 8, the system will operate as a double three-phase system, each electric valve means conducting current for electrical degrees but for only 60 electrical degrees with any other one electric valve in another group. The time at which electric valve means 9-H are rendered conductive is determined by the excitation circuits of which excitation circuit i8 is representative.

Considering the operation of excitation circuit is in particular, the capacitance 39 is energized or charged from the secondary winding 22 of transformer 2i: and is discharged through a circuit to effect energization of the immersionignitor control member I! of electric valve means 9 at the desired precise time during the cycles of applied anode-cathode voltage. The energize.- tion of the control member I! is effected by renering the electric discharge device 34 conduct ing, thereby discharging the capacitance 30. Due to the fact that capacitance 3G and inductance 32, in conjunction with the resistance 33 and electric discharge device 35, constitute an oscillatory circuit, a single unidirectional impulse of current of the proper polarity will be transmitted to the control member l'i. Furthermore, due to the fact that the natural oscillation frequency of this oscillatory circuit is substantially greater than the frequency of circuit I, this impulse will be of short duration and have a substantially perpendicular wave front. Due to the fact that the energizing circuit for the control member I! is oscillatory and because of the connection of the electric discharge device 34 and its inherent unidirectional conducting characteristics, only a single positive impulse of current will be transmitted to control member 1?. The inductance 32 serves as a means for rendering the anode of the electric discharge device 34 negative with respect to the cathode thereof, so that the control grid 35 may assume or regain control after the energization of the control member ll. As soon as an arc discharge is established Within the electric valve means 9 by the transmission of a predetermined current through the control member I, the current will be transferred to the auxiliary electrode l8 through the connection 38 due to the relatively smaller impedance which this path affords to the flow of current. The current-carrying duty imposed on control member l"! is substantially lessened, that is, the average current is reduced, resulting in more favorable conditions for an increased length of life of the electric valve means.

The operation of the control or excitation circuit 19 of Fig. 1 may be more fully explained by referring to the operating characteristics shown in Fig. 2. Curve A represents the voltage applied to the excitation circuit 19 by winding 22; curve B represents the current transmitted to the immersion-igniter control member l1, and curve C represents the current transmitted by the auxiliary electrode 53. At time a the electric discharge device 34 is rendered conducting, effecting discharge of the capacitance 30 through the circuit including inductance 32, resistance 33, electric discharge device 34 and control member i'l. At time b, the current through the immersion-ignitorcontrol member I"! has attained that value sufficient to initiate a cathode spot on the surface of the cathode i5 and to ionize the mercury vapor. Upon the initiation of the arc discharge, the current is transferred to the auxiliary electrode l8, thereby relieving the duty imposed on the control member II. The auxiliary electrode l8 thereafter conducts current until the alternating voltage of winding 22 becomes nega-- tive.

By adjustment of the rotary phase shifter 33, it is possible to control the time at which the electric valve means 9-i are rendered conducting and, hence, it is possible to control the voltage impressed across the direct current load circuit. As the times of initiation of arc discharge are retarded relative to the zero point of the positive half cycle, the voltage impressed on the direct current circuit will be decreased, and, conversely, as the time of initiation of arc discharge is advanced, the voltage impressed across the direct current circuit will be increased.

Fig. 3 is a modification of the arrangement shown in Fig. 1 and corresponding elements have been assigned like reference numerals. In Fig. 3, the inductance 32 is connected in a different portion of the excitation circuit 19. Electrode I8 is connected between resistance 33 and resistance 44. Otherwise, the system and the operation of the system are substantially the same as explained above in connection with Fig. 1.

While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and comprising electric valve means having an anode, a cathode, an immersion-ignitor control member associated with said cathode, an auxiliary electrode and employing an ionizable medium capable of supporting an arc discharge, and an excitation circuit for transmitting unidirectional impulses of current to said control member and for energizing the auxiliary electrode to maintain arc discharges after the initiation of arc discharges by the energization of the control member and comprising a capacitance and an inductance having a natural oscillation frequency substantially greater than the frequency of said alternating current circuit.

2. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and comprising electric valve means having an anode, a cathode, an immersion-ignitor control member associated with said cathode, an auxiliary electrode and employing an ionizable medium capable of supporting an arc discharge, and an excitation circuit for transmitting periodic unidirectional impulses of current to said control member and for energizing the auxiliary electrode to maintain arc discharges within said electric valve means after the initiation of are discharges by the energization of said control member comprising a capacitance, means for charging said capacitance, a discharge circuit for discharging said capacitance through said control member and comprising an inductance and an electronic discharge device, said discharge circuit having a natural oscillation frequency substantially greater than the frequency of said alternating current circuit.

3. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and comprising electric valve means having an anode, a cathode, an immersion-ignitor control member associated with said cathode, an auxiliary electrode and employing an ionizable medium capable of supporting an arc discharge, an excitation circuit for transmitting periodic unidirectional impulses of current to said control member and comprising a capacitance, means for charging said capacitance, a discharge circuit for discharging said capacitance through said control member comprising in series relation a resistance, an inductance and an electronic discharge device, and means for connecting said auxiliary electrode to the common juncture of said resistance and said inductance to effect transfer of current each cycle from said control member to said auxiliary electrode upon the initiation of an arc discharge within said electric valve means,

4. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and comprising electric valve means having an anode, a cathode, an immersion-ignitor control member associated with said cathode, an auxiliary electrode and employing an ionizable medium capable of supporting an arc discharge, an excitation circuit for transmitting periodic unidirectional impulses of current to said control member to render said electric valve means conductive periodically and comprising a capacitance, means for charging said capacitance, a discharge circuit for said capacitance to discharge said capacitance through said control member and comprising in series relation a resistance, an inductance and a unidirectional conducting device, and means connected'between said auxiliary electrode and the common juncture of said resistance and said inductance to transfer current each cycle from said control member to said auxiliary electrode upon the initiation of an arc discharge within said electric valve means.

5. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and comprising electric valve means having an anode, a cathode, an immersion-ignitor control member associated with said cathode, an auxiliary electrode and employing an ionizable medium capable of supporting an arc discharge, an excitation circuit for transmitting periodic unidirectional impulses of current to said control member to render said electric valve means conductive periodically and comprising a capacitance, means for charging said capacitance, an oscillatory discharge circuit for discharging said capacitance through said control member and comprising an inductance and a unidirectional conducting device, and means for connecting said auxiliary electrode to said discharge circuit to effect transfer of current each cycle from said control member to said auxiliary electrode upon the initiation of an arc discharge within said electric valve means.

6. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and comprising electric valve means having an anode,

a cathode, an immersion-ignitor control member, an auxiliary electrode and employing an ionizable medium capable of supporting an arc discharge, an excitation circuit for transmitting periodic unidirectional impulses of current to said control member to render said electric valve means conductive periodically and comprising a capacitance, means for charging said capacitance, an oscillatory discharge circuit for discharging said capacitance through said control member and comprising a pair of serially connectcd resistances, a unidirectional conducting device and an inductance all connected in series relation with said control member, and means for connecting said auxiliary electrode to the common juncture of said resistances to eifect transfer of current each cycle from said control member to said auxiliary electrode upon the initiation of an arc discharge within said electric valve means.

'7. In combination, an alternating current circult, a direct current circuit, electric translating apparatus connected between said circuits and comprising electric valve means employing an ionizable medium capable of supporting an arc discharge and having an anode, a cathode, an immersion-ignitor control member associated with said cathode and an auxiliary electrode, means for transmitting periodic impulses of unidirectional current to said control member comprising a capacitance and an oscillatory discharge circuit for said capacitance comprising an inductance and an electronic discharge device connected in series relation with said control memher, the auxiliary electrode being connected in circuit with said electronic discharge device to effect transfer of current from said control member to said auxiliary electrode during each cycle of applied anode-cathode voltage upon the initiation of an arc discharge within said electric 20 valve means. 

